Medical practitioners, such as doctors, surgeons, and other medical professionals, often rely upon technology when performing a medical procedure, such as image-guided surgery or examination. A tracking or navigation system may provide positioning information for a medical instrument with respect to the patient or a reference coordinate system, for example. A medical practitioner may refer to the navigation system to ascertain the position of the medical instrument when the instrument is not within the practitioner's line of sight. A tracking system may also aid in pre-surgical planning.
The tracking or navigation system allows the medical practitioner to visualize the patient's anatomy and track the position and orientation of the instrument. The medical practitioner may use the tracking system to determine when the instrument is positioned in a desired location or at a desired orientation. The medical practitioner may locate and operate on a desired or injured area while avoiding other structures. Increased precision in locating medical instruments within a patient may provide for a less invasive medical procedure by facilitating improved control over smaller instruments having less impact on the patient. Improved control and precision with smaller, more refined instruments may also reduce risks associated with more invasive procedures such as open surgery.
Tracking systems can include ultrasound, inertial position, optical, or electromagnetic tracking systems, for example. Electromagnetic (EM) tracking systems may employ coils as receivers and transmitters. Typically, an EM tracking system is configured using an industry-standard coil architecture (ISCA). ISCA uses three co-located orthogonal, quasi-dipole transmitter coils and three co-located quasi-dipole receiver coils. Other systems may use three large, non-dipole, non-co-located transmitter coils with three co-located quasi-dipole receiver coils. Another tracking system architecture uses an array of six or more transmitter coils spread out in space and one or more quasi-dipole receiver coils. Alternatively, a single quasi-dipole transmitter coil may be used with an array of six or more receivers spread out in space.
Tracking accuracy, navigable range, and metal tolerance are three challenging and often conflicting concerns to be addressed when designing an EM tracking system. For fluoroscope-based two-dimensional image navigation applications, both tracking volume (e.g., transmitter to receiver distance) and metal distortion can be managed by users via adjustment of an image intensifier with a calibration target attachment (e.g., fiducial markers, EM receiver, and shield) closer to a patient anatomy where a transmitter is usually placed.
For three-dimensional image navigation applications, however, the transmitter-to-calibration target receiver distance varies as the C-arm is rotated to different positions. Users generally have limited control of transmitter placements depending on various clinical applications to fulfill a tracker range requirement. As the position of the C-arm keeps changing during a spin, there is a chance of losing the tracker data due to table interference or due to the transmitter going out of range.
In an example, the navigation coverage may be increased by increasing the tracker range. However increasing the tracker range generally requires an increase of the transmitter size and results in significant hardware changes. Also, this solution will not solve the problem of EM interference caused by the presence of surgical or patient tables, which are generally made with significant amounts of metals.
Alternatively, the tracker field of view may be increased by distributing an array of EM receivers on the X-ray detector. The table interference can be minimized to some degree by using the least distorted tracker readings obtained from the sensor with the largest distance from the table at a 3D rotation position. This, however, may increase system complexity since it requires additional A/D electronics for multiple channel signal acquisition, and a complicated computer algorithm for determining optimal sensor outputs.
Thus there exists a need to restore the tracking information lost in a three-dimensional (3-D) image acquisition spin. It would be desirable to provide a system and method for automatically restoring tracking information or navigation data loss in an image guided system.